ACCA article – Throughput accounting and the theory of constraints, part 2

Hi everyone,

I’m currently going through Example 2 on the acca article and I don’t understand where they get the figure of 600 when calculating additional sales on option to buy Z (table 2), the figure of 800 on the option to buy both Z and Y, and finally 1000 on the option to buy Z, Y and X.

Any ideas?

Many thanks in advance